Radio frequency identification (RFID) tags are tags with small integrated circuits which may be attached to containers, packages, or individual goods. They are used to store information about the item such as price, serial number, and shipping information (including tracking number, shipping date, arrival date, as well as other information). RFID tags generally include an RFID signal transmitter which generates an RFID signal. In general, the RFID signal transmitter detects a reader interrogation signal and replies by transmitting a response signal that contains the information stored in the RFID transmitter. The reader detects the response signal from the RFID signal transmitter and stores the information in its memory. Some RFID tags contain a battery, while others store the energy of received interrogation signals and use that energy to power their circuits.
Environmental, material, and electromagnetic conditions may affect the performance of RFID tags and RFID signal transmitters. Different physical mechanisms that affect the propagation of electromagnetic or radio waves include reflection or scattering, absorption, spreading loss, and interference. In a space free of any obstructions or absorption mechanisms, the strength of an RFID signal declines in inverse proportion to the square of the distance. For an electromagnetic wave propagating through a region in which reflections can arise from the ground and from obstacles (particularly metal or liquid obstacles), the reduction in strength is greater and can vary considerably. The disruptive materials may be the goods within their packaging, the surface of the goods themselves, or the walls of the exterior container. Additionally, environmental conditions, especially “noise” from other systems (including mechanical and electrical noise), may also interfere with signal reception or signal recognition. Moreover, the RFID tag may be absent (i.e., missing or stolen) or present but not operable.
For these reasons mentioned above, as well as other reasons, a reader interrogation signal is often not received or recognized by the RFID signal transmitter. And, similarly, the response signal from the RFID signal transmitter is often not received or recognized by the reader. This means that the contents of the container, the composition of the container, and the interrogation environment can influence whether 100% tag readability can be achieved in practice. Although currently available tags are effective at transmitting information, they fail to provide a mechanism for tracking signal transmissions to allow system operators to re-scan, re-position, or otherwise manually recognize and record product information that was previously not recognized by the RFID system.